This invention relates to the cooling of an airfoil comprising a portion of a stator vane or nozzle of the first stage of a gas turbine engine; and more particularly, to the hole pattern formation in the airfoil for thin film cooling of a trailing edge of the airfoil.
In the construction of gas turbine engines, an annular array of turbine segments is provided to form a turbine stage. Generally, the turbine stage is defined by outer and inner annular bands spaced apart from each other with a plurality of vanes or airfoils extending between the bands and circumferentially spaced from one other. This construction, in turn, defines a path for a working fluid flowing through the turbine. In a gas turbine engine, this is a hot gas. As will be appreciated by those skilled in the art, the most extreme adverse operating conditions are generally encountered at the first stage of the turbine. That is because this stage is immediately downstream of the engine's combustion chamber and components comprising this stage must therefore withstand high thermal loads. As is known in the art, cooling systems for this engine stage utilize thin film cooling techniques to insure so adequate cooling is provided. Thin film cooling is accomplished by discharging air through orifices formed in portions of the nozzle. The discharged air then forms a protective thin film boundary layer between the hot stream of gases flowing through the first stage of the turbine and the surface of the nozzle.
Various problems with thin film cooling systems have been encountered and solutions to these problems have been addressed in U.S. Pat. Nos. 6,583,526, 6,561,757, 6,553,665, 6,527,274, 6,517,312, 6,506,013, 6,435,814, 6,402,466, 6,398,486, and 5,591,002, all of which are assigned to the same assignee as the present application.
The present invention is directed to an advanced film-cooling configuration for cooling the trailing edge of a nozzle used in the first stage of an advanced design gas turbine engine. The nozzle is a steam cooled component which operates at firing temperatures which require cooling of the airfoil to extend the low cycle fatigue (LCF), oxidation, and creep life of the component. While steam adequately cools the majority of the nozzle, it is not feasible for use in cooling the trailing edge of the nozzle. Rather, this requires a novel and advanced thin film cooling configuration in order for the trailing edge to not rapidly deteriorate once the turbine is in service which would require costly servicing or replacement of the nozzle and unacceptable down-time when the turbine is out of service.